Field of the Invention
The present invention relates to an image capture apparatus and a method for controlling an image capture apparatus, and relates in particular to an automatic focus detection technique.
Description of the Related Art
As automatic focus detection (AF) systems of an image capture apparatus, a contrast AF system and a phase-difference detection AF system are known. Both the contrast AF system and the phase-difference detection AF system are AF systems that are often used in video cameras and digital still cameras, and in some of these AF systems, an image sensor is used as a focus detection sensor.
In these AF systems, focus detection is performed using an optical image, and accordingly there are cases where an aberration of an optical system that forms the optical image causes an error in a focus detection result. A method for reducing this kind of error has been proposed.
Patent Document 1 (Japanese Patent No. 5087077) discloses a method in which reference correction data defining a combination of a plurality of representative values is prepared for each of an AF frame, a focal length, an AF evaluation frequency, and the distance to a subject, and corrects a focus detection result using correction data obtained by performing interpolation in accordance with an actual condition.
However, with the method in Patent Document 1 that uses a correction value suitable for the AF evaluation frequency unique to a camera body to correct the focus detection result, a problem arises in that a focus detection error cannot be sufficiently corrected. The focus detection error originally is a difference between a focus condition under which an observer feels most favorable with respect to a captured image and a focus condition indicated by the focus detection result. However, in the method described in Patent Document 1, the focus condition of the captured image is not considered.
Also, the AF evaluation frequency in Patent Document 1 represents spatial frequency characteristics of a single frequency. However, the band to be actually evaluated in focus detection has a frequency bandwidth, and does not represent only characteristics of a single frequency.